Anti-flex-cracking agent



' Rubber Carbon black Softener 7 V Tensile strength, lbs/sq. in

Patented Nov. 16, 19:43,

Robert'T. Armstrong, Radburn, N. L, assignor to United States Rubber Company, New York,

, N Y., a corporation of New Jersey No Drawing. Application December 19, 1940, seriainasmsis 5 Claims. 260-810) This invention relates to improvements in antiflex-cracking agents for rubber andrubber-like materials, and to the products containing said agents.

An object of the invention is to provide cheap available chemicals which have been found to possess the property ofinhibiting fatigue failure amounts varying from 0.1% to by weight or cracking due to repeated fiexings of rubber,

and with substantially no discoloration of the rubber when it is exposed to atmosphere and sunlight. Other objects willbe' apparent from,

the following description.

Broadly the invention comprises incorporating in a rubber composition a para-tertiary'alkyl phenol as an anti-flex cracking agent. .Among the better known chemicals of this class are p tertiary butyl phenol OH: OHZI H: p and p-tertiary amyl phenol I CHa' although others in the class with longer openchain structures may also be used.

The data in the following table illustrates the property of these chemicals to inhibit fatigue failure due to repeated flexings of the rubber and compared with use of phenol itself. The chemical (1% based on the rubber) was added on a laboraresults on compound C show a marked improvement by the use of apara-tertiary-alkyl phenol.

correspondingly greater improvements are ob- 1 tained by using larger proportions of para-tertiarybut'yl phenol.

The anti-flex cracking agents may be used in based on the rubber or rubber-like material.

It is to be understood that while in the example of rubber mixes given above certain vulcanizing ingredients are disclosed, the invention is not limited thereto but may be carriedfout by the use of othersuitable vulcanizing agents, fillers,

acceleratora 'etc. The anti-flex cracking agent may be incorporated in the rubber'on the mill,

. orincorporated therein by diffusion from solution containing the agent, or otherwise. 7

With the disclosure given above, it is obvious that modificationswill suggest themselves, for

example other rubbers than caoutchouc rubbers, V namely thoserubbers which are artificially pre-' pared to simulate the elastic properties of ordi- 7 nary rubber, may likewise be treated according tory mill at approximately 180 F. to a typical tire tread compound (A) containing by weight:

Zinc (JXl dP 2 Accelerator" 1 Sulfur t r Slabs onetenth-inch thick were cured 35minutes at 146.5 C. in a mold, and samples cut from the cured slabs were flexed to failure.

-Tertiary p butyl Phenol (l- 3, 300 4, 200 Flexing l to failure 61 "1 Standard De Mattia flexing test: 300 cycles/min. throughe. "hair-pin bend to 100% elongation, at room temperature.

Comparison ofthe results on compound A with those on compound B shows that phenol itself does not inhibit the fatigue failure, whereas the to the invention, and it is not desired to limit theinvention otherwise than as set forth in the appended claims. 7 1

Having thus described my invention, what I claim and desire to protect byLetters Patent is: 1. A process of improving the flex-cracking properties, of rubber compositions designed for repeated flexing during use, which comprises incorporating therein as an anti-flex-cracking agent a phenol, the position para to the phenolic hydroxyl group being occupied by'a tertiary alkyl group.

2. A process of improving the flex-cracking properties of rubber compositions designed for,

repeated flexing during use, which comprises incorporating therein as an anti-flex-cracking agent a compound having the formula where A is a tertiary alkyl group, and curing the rubber. I

3. A process of improving the flex-cracking properties of rubber compositions designed for repeatedfiexing during use, which comprises incorporating therein as an. anti-fiex-cracking agent, p-tertiary' butyl phenol.

4.. A process of improving the flex-cracking properties of rubber compositions designed for repeated flexing during use, which comprises incorporating therein as an anti-flex-cracking agent, p-tertiary-amyl phenol.

5. A vulcanized product of a rubber composition containinga para-tertiary-alkyl phenol as an anti-flex cracking agent.

ROBERT 'I'. ARMSTRONG. 

